A variety of production fluids are pumped from subterranean environments. Different types of submersible pumping systems may be disposed in production fluid deposits at subterranean locations to pump the desired fluids to the surface of the earth.
For example, in producing petroleum and other useful fluids from production wells, it is generally known to provide a submersible pumping system for raising the fluids collected in a well. Production fluids, e.g. petroleum, enter a wellbore drilled adjacent a production formation. Fluids contained in the formation collect in the wellbore and are raised by the submersible pumping system to a collection point at or above the surface of the earth.
A typical submersible pumping system comprises several components, such as a submersible electric motor that supplies energy to a submersible pump. The system further may comprise a variety of additional components, such as a connector used to connect the submersible pumping system to a deployment system. Conventional deployment systems include production tubing, cable and coiled tubing. Additionally, power is supplied to the submersible electric motor via a power cable that runs through or along the deployment system.
Often, the subterranean environment (specifically the well fluid) and fluids that are injected from the surface into the wellbore (such as acid treatments) contain corrosive compounds that may include CO2, H2S and brine water. These corrosive agents can be detrimental to components of the submersible pumping system, particularly to internal electric motor components, such as copper windings and bronze bearings. Moreover, irrespective of whether or not the fluid is corrosive, if the fluid enters the motor and mixes with the motor oil, the fluid can degrade the dielectric properties of the motor oil and the insulating materials of the motor components. Accordingly, it is highly desirable to keep these external fluids out of the internal motor fluid and components of the motor.
Submersible electric motors are difficult to protect from corrosive agents and external fluids because of their design requirements that allow use in the subterranean environment. A typical submersible motor is internally filled with a fluid, such as a dielectric oil, that facilitates cooling and lubrication of the motor during operation. As the motor operates, however, heat is generated, which, in turn, heats the internal motor fluid causing expansion of the oil. Conversely, the motor cools and the motor fluid contracts when the submersible pumping system is not being used.
In many applications, submersible electric motors are subject to considerable temperature variations due to the subterranean environment, injected fluids, and other internal and external factors. These temperature variations may cause undesirable fluid expansion and contraction and damage to the motor components. For example, the high temperatures common to subterranean environments may cause the motor fluid to expand excessively and cause leakage and other mechanical damage to the motor components. These high temperatures also may destroy or weaken the seals, insulating materials, and other components of the submersible pumping system. Similarly, undesirable fluid expansion and motor damage can also result from the injection of high-temperature fluids, such as steam, into the submersible pumping system.
Accordingly, this type of submersible motor benefits from a motor fluid expansion system able to accommodate the expanding and contracting motor fluid. The internal pressure of the motor must be allowed to equalize or at least substantially equalize with the surrounding pressure found within the wellbore. As a result, it becomes difficult to prevent the ingress of external fluids into the motor fluid and internal motor components.
Numerous types of motor protectors have been designed and used in isolating submersible motors while permitting expansion and contraction of the internal motor fluid. A variety of elastomeric bladders alone or in combination with labyrinth sections have been used as a barrier between the well fluid and the motor fluid. For example, expandable elastomeric bags or bladders have been used in series to prevent mixing of wellbore fluid with motor fluid while permitting expansion and contraction of the motor fluid.
In this latter design, the motor protector includes a pair of chambers each of which have an elastomeric bladder. The first bladder is disposed in a first chamber of the pair of chambers and includes an interior in fluid communication with the motor. This fluid communication permits motor oil to flow from the motor into the elastomeric bladder during expansion and to flow from the elastomeric bladder back to the motor during contraction.
The second chamber also has an expandable bladder, filled with motor oil, which is in fluid communication with the first chamber but external to the first elastomeric bladder. The second chamber is vented or open to the wellbore environment. This assembly permits fluid to flow between the second elastomeric bladder and the adjacent chamber as the first elastomeric bladder expands or contracts. Simultaneously, wellbore fluid is allowed to flow in and out of the second chamber, external to the second elastomeric bladder, to permit equalization of pressure as the second bladder expands and contracts.
This type of expansion chamber works well in many environments, but certain of the corrosive agents found in at least some wellbore environments comprise corrosive gases that permeate the elastomeric bags or bladders. These corrosive agents eventually can work their way into the motor oil within the first elastomeric bladder and ultimately corrode and damage internal components of the electric motor. The wellbore environment also may have an undesirable temperature (e.g., hot), which may destroy the elastomeric bag or bladder and the shaft seal materials throughout the submersible pumping system.
The conventional labyrinth type protector uses the difference in specific gravity of the well fluid and the motor fluid to separate the fluids. For example, a typical labyrinth may embody a chamber having a first passageway to the motor fluid and a second passageway to an undesirable fluid, such as fluids in the wellbore. The first and second passageways are generally oriented on opposite sides of the chamber to maintain fluid separation in a vertical orientation. Accordingly, conventional labyrinth type protectors are generally less effective, or totally useless, in orientations deviated from the vertical orientation.
Accordingly, the need exists for improved motor protectors, which are operable in variable temperature applications and multiple orientations. For example, it would be advantageous to position a bellows assembly between a motor fluid and an external fluid and positively pressurize the motor fluid relative to the external fluid to prevent inward leakage of the external fluid into the motor. It also would be advantageous to provide a relatively balanced bellows assembly having one or both ends fixed, rather than using sliding seals. Moreover, it would be advantageous to provide a multi-orientable labyrinth having conduits extending in multiple orientations to maintain fluid paths having peaks and valleys in all potential orientations.